/Engine/Source/Runtime/MediaUtils/Public/MediaSamples.h
Remove any caption samples from the queue that have no chance of being displayed anymore
virtual uint32 PurgeOutdatedMetadataSamples ( const [FMediaTimeStamp](API\Runtime\Media\FMediaTimeStamp) & ReferenceTime, bool bReversed, [FTimespan](API\Runtime\Core\Misc\FTimespan) MaxAge )